1. Field of Invention
The present invention relates to a semiconductor process. More particularly, the present invention relates to a method for forming a void-free dielectric layer.
2. Description of Related Art
FIG. 1 is a schematic, cross-sectional view of a conventional deposition process. As shown in FIG. 1, a substrate 100 and a metal pattern 102 over the substrate 100 are provided, and they are covered with a high density plasma (HDP) dielectric layer 104. The HDP dielectric layer 104 often has several sharp corners 105 on its surface over the metal pattern 102.
Still referring to FIG. 1, a deposition layer 106 is formed over the HDP dielectric layer 104. The deposition layer 106 is conventionally made of a low-cost material, such as a silane-based (SiH.sub.4 -based) material. However, the SiH.sub.4 -based material has poor step coverage on the sharp corners 105, and therefore has voids 120 therein after it is deposited over the HDP dielectric layer 104. The voids 120 are easily exposed and filled with polishing slurry in the following chemical-mechanical polishing step. This polishing slurry in the voids affects the electricity, yield and reliability of the deposition layer 106.
Moreover, in the following via process, the voids 120 are defect sources on the vertical sidewall of the via hole. Those defects on the sidewalls often induce `volcanoes` when a tungsten plug is formed on a barrier layer over the via hole. The volcanoes, which are rapid reactions between the titanium (Ti) barrier layer and tungsten fluoride (WF.sub.6, a tungsten plug material source), often cause via hole failures in the via process.
Although forming the deposition layer from a material with good step coverage inhibits void formation, it costs much more than forming the deposition layer from a SiH.sub.4 -based material.
Forming the deposition layer by high density plasma (HDP) deposition also inhibits void formation. However, the HDP deposition is a high-cost technique, and is also a technique that easily charge damages the underlying features on the substrate.